Schematic for a Rocktron Nitro pedal

[pbdog]

I'm trying to fix one.thanks pb

[TWANG]

I need one, too.
I want to adjust the treble.

[Mark Hammer]

Looks like a pretty simple pedal. Just one more booster. Tell us a bit about what's inside it, or post a pic of the board, and I'll tell what to look for.

[TWANG]

thanks!

here's some pics

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open that in it's own page and it blows up

I put a Mallory in for C10 just for the heck of it.. had the right value.
thinking I may as well replace the ceramics with silver mica while I'm in there.

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part list.

C1: 10µF
C2: 10µF
C3: 100µF
C4: 10µF
C5: 10µF
C6: 104
C7: 101
C8: 2A104J
C9: 2A104J
C10: 2A103J
C11: 101
C12: 104

R1: 82 or 820 (I'd say 820)
R2: 1M
R3: 100K
R4: 100R
R5: 100K
R6: 1K (LED res?)
R7: 100K
R8: 22K
R10: 100R
R11: 100K
R12: 1K
R13: 100R
R14: 1M
R15: 100K
R17: 100R

D1: 1N4148?
pot: B500K
U1: NE5532N
Q1: MPF102
Q2: 7805

[Sock Puppet]

Here's one from a thread on freestompboxes.

Rocktron_Nitro_Booster.pdf

[TWANG]

fantastic..
I tried to find that there, too.. and couldn't.

[Mark Hammer]

Thanks for the info, guys.

Okay, so what do you want to do with the treble, Twang? If the intent is to tame the treble, then replace C7 (10pf) with a 100pf cap). That will tame the treble so that your rolloff starts around 3.3khz at max boost, and a bit higher up as the boost amount is turned down. People generally want a "rounder" signal when pummeling their amp.

If you want more treble bite, then stick a 2200pf cap and 47k resistor in series, and place them in parallel with R11 (100k). That will provide more gain for content above 1.6khz or so at all settings. With that extra gain, you'll likely want to make C7 22-39pf, just to keep the hiss under control.

[TWANG]

The formula for calculating the needed cap value for C7 is F = 1 /[2 * pi * Rmeg * Cuf]. I used the max gain setting (where RP1 = 500k) to determine the value.

With RP1 + R8 = 522k, you get the following rolloffs at max gain:
with C7 = 47pf, rolloff starts around 6.5khz
with C7 = 68pf, rolloff starts around 4.5khz
with C7 = 82pf, rolloff starts around 3.7khz

Note that these ar 6db/oct rolloffs, such that there is still plenty of treble above the rolloff frequency, just less of it. If you need the rolloff to be sharper, you can always play with the value of C11 as well. Both C11 and C7 are set to provide mximum bandwidth without irritating hiss and other HF noise. No reason why you can't make them do double duty. Consider increasing C11 to 470pf to help in the "de-edging" of the pedal.

Note that capacitor values sum in parallel. This means that if you identify the solder pads for these parts, you can experiment tonally, by temporarily soldering on additional caps on the copper side of the board, listening to the result, and "seasoning to taste". I do it all the time. Just be prudent with your soldering/unsoldering so you don't damage the board.

[TWANG]

I put a 22pf silver mica in and it increased the treble considerably.
the ceramic was marked 10
I don't know how to read values on those things since I never use them..
so I'll try a 100pf on it next and just do the experiment..
and try messing with c11, too

[TWANG]

100pf silver mica C7
500pF silver mica C11

it's just way bright.
Even 1/2 way up..

I'm sure the silver micas sound better though.. I'll say that.
but man... way too bright for me.

[TWANG]

Here's where I wound up..
C7 22pF
C11 100pF
both silver micas
C10 up to .1uF
Mallory.

Now the pedal is very close to the tone the guitar straight into the amp makes.
Wouldn't mind if it were still a tick less highs, or a slight mid boost, but I'll settle for this.

It's an always on pedal unless you have something else in there because off it mutes the tone like mad.

[Mark Hammer]

How a higher value of C7 yields more treble is a mystery to me, not unless you're reading the values wrong. You'll forgive if I underestimate your knowledge/chops. With silver micas, they are often stated in terms of the last digit being the number of zeros. So, the 51pf caps in my parts bin say 510 on them, and the 68pf ones say 680, the last digit indicating that there are no zeroes after the 51 or 68. Quite possible your "100pf" was actually 10pf. Certainly consider other values, and don't be shy about using ceramic caps. This is a low voltage application. I can't imagine that use of ceramic would impact on tone in any substantive way.

Assuming the posted schematic is correct, with C7=22pf at max gain the rolloff starts around 13.8khz, and at half gain the rolloff is at roughly twice that frequency. Hardly a treble-taming in my estimation. Particularly since a lot of guitar speakers roll off around 6khz in the first place.

Of course, what matters is whether it sounds the way you like, and not what the calculations on paper say. The swapping of a .1uf cap for the stock .01uf value of C10 is reasonable.

[TWANG]

you can question my knowledge anytime, and I'll appreciate it!
For example thanks for clearing up the values reading.
I was taking 500 as meaning 500pf on the silver micas.. and now I find out they are 50?
I was pretty sure I ordered 500pF from mouser..so I'm confusamacated there.

I'm going to put them on the meter.. and then try to raise C7 to 100pF and give it a listen.

And then I'll get back in here for some more lesson!

[TWANG]

Ok

I've got The C10 in at .1uF.
I'll go out now and put in higher values for C7 and C11
and I've got the amp running and I'll definitely be able to hear this.

My feeling is that changing those two caps does zip.

[TWANG]

OKey dokey then
I had the C7 at 500pf
and the C11 at .022uF

I swapped in 100pF.. tested on my meter as .1nF
for C7
and I swapped in 500pF.. tested as .5nF on my meter
for C11.

I really heard no difference between this and the values I had in.

It's brighter than the guitar plugged straight into the same output.. with pedal and volume levels set the same.
The only thing that made a difference at all was the C10 swap.

The caps that read 100 are in fact, 100pf, etc.
all silver micas I don't have many ceramic chips here and generally toss 'em away if I pull them.

So.. I can't explain this. But that's what I've done and what I heard.